The greatest part about this technique is the ability to watch the piece as it reduces and decide for yourself when the color is to your liking. I personally stick with simple thrown shapes of even thickness made with a clay suitable to withstand the raku process. It should be made from a clay with a decent amount of sand and/or grog to help it withstand the thermal shock of rapid heating and cooling. This process has many crucial steps that have to be executed just right in order to insure a successful firing. Set up everything in advance.
Have your bisque pieces glazed in a moderate to heavy application of copper wash(see below). I apply mine with a spray gun outdoors or in a approved glaze spray booth. The next step is setting up the reduction chamber.
The reduction chamber consists of a metal tub or shallow trash can full of playground sand and a stainless steel bowl nestled inside of the sand. The bowl should have an inch of sand in the bottom and a dozen pine needles on top of the sand to help start a fire. The other piece of equipment is a glass pyrex bowl used to cover the ware after it has been put into the stainless steel bowl. Different sizes of these bowls can be used depending on the sizes of ware being fired(see pictures below). You will also need a banding wheel or heat resistant turntable, raku tongs, pine needles and a garden sprayer filled with 91% isopropyl alcohol(rubbing alcohol 91%).
Firing- Place pieces in a raku kiln and heat to 1750 F’. A pyrometer or pyrometric cone is needed because the copper wash will appear black in the kiln even at red hot temperatures. When at the correct temperature, remove from kiln and place on banding wheel. CAREFULLY spray 7 or so layers of the alcohol on the piece waiting a few moments in between each application. Keep a decent distance and wear appropriate gloves and clothing FIRE WILL ERUPT DURING EVERY SPRAY OF ALCOHOL. Remember to turn the wheel and spray evenly. This part is amazingly fun and multiple colors will be seen dancing on the piece. When enough has been sprayed place the piece in the metal bowl in the tub. When the pine needle flame ignites, immediately cap it with the glass bowl and cover the edges with sand to make an airtight seal. After a minute or so when the piece is all one copper color quickly lift one edge of the glass bowl and give it a quick spray of alcohol and quickly close again and cover with sand. The colors will reappear while the alcohol burns and the oxygen is reduced. After about ten minutes, or whenever the piece reaches the color you desire, remove from tub, return to the banding wheel, and spray with water to set the color. When the piece is cool a tile sealant will need to be applied to prevent the copper from oxidizing and turning your piece back to black over time.